class Solution {
public:
    int findMaxLength(vector<int>& nums) {
        unordered_map<int,int> hash;
        hash[0]=-1;
        int sum=0,ret=0;
        for(int i=0;i<nums.size();i++)
        {
            sum+=nums[i]==0?-1:1;
            if(hash.count(sum))
            ret=max(ret,i-hash[sum]);
            else
            hash[sum]=i;
        }
        return ret;
    }
};